The invention provides for methods to convert vegetable and/or animal oils (e.g. soybean oil) to highly functionalized alcohols in essentially quantitative yields by an ozonolysis process. The functionalized alcohols are useful for further reaction to produce polyesters and polyurethanes. The invention provides a process that is able to utilize renewable resources such as oils and fats derived from plants and animals.
Polyols are very useful for the production of polyurethane-based coatings and foams as well as polyester applications. Soybean oil, which is composed primarily of unsaturated fatty acids, is a potential precursor for the production of polyols by adding hydroxyl functionality to its numerous double bonds. It is desirable that this hydroxyl functionality be primary rather than secondary to achieve enhanced polyol reactivity in the preparation of polyurethanes and polyesters from isocyanates and carboxylic acids, anhydrides, acid chlorides or esters, respectively. One disadvantage of soybean oil that needs a viable solution is the fact that about 16 percent of its fatty acids are saturated and thus not readily amenable to hydroxylation.
One type of soybean oil modification described in the literature uses hydroformylation to add hydrogen and formyl groups across its double bonds, followed by reduction of these formyl groups to hydroxymethyl groups. Whereas this approach does produce primary hydroxyl groups, disadvantages include the fact that expensive transition metal catalysts are needed in both steps and only one hydroxyl group is introduced per original double bond. Monohydroxylation of soybean oil by epoxidation followed by hydrogenation or direct double bond hydration (typically accompanied with undesired triglyceride hydrolysis) results in generation of one secondary hydroxyl group per original double bond. The addition of two hydroxyl groups across soybean oil's double bonds (dihydroxylation) either requires transition metal catalysis or stoichiometric use of expensive reagents such as permanganate while generating secondary rather than primary hydroxyl groups.
The literature discloses the low temperature ozonolysis of alkenes with simple alcohols and boron trifluoride catalyst followed by reflux to produce esters. See J. Neumeister, et al., Angew. Chem. Int. Ed., Vol. 17, p. 939, (1978) and J. L. Sebedio, et al., Chemistry and Physics of Lipids, Vol. 35, p. 21 (1984). A probable mechanism for the low temperature ozonolysis discussed above is shown in FIG. 1. They have shown that a molozonide is generated at relatively low temperatures in the presence of an alcohol and a Bronsted or Lewis acid and that the aldehyde can be captured by conversion to its acetal and the carbonyl oxide can be captured by conversion to an alkoxy hydroperoxide. In the presence of ozone the aldehyde acetal is converted to the corresponding hydrotrioxide at relatively low temperatures. If the reaction temperature is then raised to general reflux temperature, the hydrotrioxide fragments to form an ester by loss of oxygen and one equivalent of original alcohol. At elevated temperatures, and in the presence of an acid such as boron trifluoride, the alkoxy hydroperoxide will eliminate water to also form an ester in essentially quantitative yields. This overall process converts each olefinic carbon to the carbonyl carbon of an ester group so that two ester groups are produced from each double bond.